Small human-occupied, man-made environments that are used or immersed in harsh ambient environments may require heating or cooling in order to provide safe and comfortable temperature conditions for their human occupant(s). For example, garments worn by divers, firefighters, chemical “hazmat” workers, etc., frequently must be heated or cooled depending on ambient environmental conditions. In addition, small chambers such as dive chambers or hyperbaric chambers must also be heated or cooled. In each of these cases, constraints on size, weight, power availability and/or power consumption limit the types of heating or cooling systems that can be used. Furthermore, since some applications of these human-occupied environments may require heating while other applications may require cooling, it is advantageous to have a single system that is capable of being configured for heating or cooling as dictated by the particular application conditions.